html {
  margin-bottom: 2vw;
}
body {
  margin: 0;
}
div {
  float: left;
  width: calc(92vw / 3);
  height: calc(92vw / 3);
  margin: 2vw 0  0 2vw;
  border-radius: 3vw;
  /* 定义动画的属性 */
  animation: myfirst 6s infinite alternate;
}
/* 声明动画的细节 */
@keyframes myfirst {
  0%   {border-radius: 3vw;background: gold;transform: rotate(0deg);}
  50%  {border-radius: 15vw;background: #999999;transform: rotate(45deg);}
  100% {border-radius: 9vw;background: black;transform: rotate(90deg);}
}
/* 隐藏滚动条,仅支持Webkit内核浏览器 */
::-webkit-scrollbar{
  display:none;
}